FIG. 22 is a block diagram showing the configuration of the data distribution management system in which a conventional data distribution management device is used (refer to Study Report 98-DPS-89-12 of the Information Processing Society of Japan). As in FIG. 22, this data distribution management system is provided with a transmission device C11, a receiving device C12, and a transmission gateway 100 which is connected to both the transmission device C11 and the receiving device C12 through respective circuit L11 and circuit L12 through which communications are performed based on TCP. Compared to the circuit L11, the circuit L12 is a circuit that, like satellite circuits, for example, is large in transmission delay.
In FIG. 22, the transmission device C11 is provided with a data packet output section 111 that outputs data packets and a temporary delivery acknowledgement receiving section 112 that receives a temporary delivery acknowledgement that the transmission gateway 100 prepares. The transmission gateway 100 is provided with not only a buffer 101 and a distribution management table 102 but also a storage section 103 that receives the data packets transmitted from the transmission device C11 and stores these data packets in the buffer 101, an output section 104 that outputs those data packets stored in the buffer 101 to the receiving device C11 through the circuit L12, a temporary delivery acknowledgement preparation section 105 which prepares a temporary delivery acknowledgement corresponding to the data packets transmitted to the receiving device C11, a temporary delivery acknowledgement transmission section 106 that transmits this prepared delivery acknowledgement to the transmission device C11, a delivery acknowledgement receiving section 107 that receives a delivery acknowledgement sent from the receiving device C11, a distribution information recording control section 108 that obtains communications information from received SYN packets and records them in the distribution management table 102 as distribution information, and a retransmission processing section 109 that performs retransmission of the data packets. Further, the receiving device C11 has a data packet receiving section 121 provided to receive data packets from the transmission gateway 100 and has also a delivery acknowledgement output section 122 provided to output a delivery acknowledgement to the transmission gateway 100.
When data packets are sent out from the transmission device C11, the transmission gateway 100 temporarily stores the received data packets in the buffer 101 and simultaneously enters the data packet in the distribution management table 102. The transmission gateway 100 transfers the data packet received from the transmission device C11 to the receiving device C12 through circuit L12 and prepares a temporary delivery acknowledgement data packet corresponding to the data packet and transmits this temporary delivery acknowledgement to the transmission device C11.
On receipt of the data packet from the transmission gateway 100, the receiving device C12 prepares a delivery acknowledgement corresponding to the received data packet and transmits this delivery acknowledgement to the transmission gateway 100. This delivery acknowledgement includes data that concerns corresponding data packets and another set of data concerning confirmation as to whether those data packets have been delivered. When the transmission gateway 100 has received the delivery acknowledgement from the receiving device C12, the transmission gateway 100 clears the data packets which are retained in the transmission gateway 100 and which correspond to this delivery acknowledgement.
Should it happen in the process of transmitting a data packet from the transmission gateway 100 to the receiving device C12, that the transfer of this data packet fails and that the receiving device C12 consequentially fails to receive this data packet, then the transmission gateway 100 receives an identical delivery acknowledgement three times on end from the receiving device C12 and retransfers the data packet.
Thus, under the conventional data distribution management system, the transmission gateway 100 sends a temporary delivery acknowledgement (tmpACK) to the transmission device C11 at the same time as the transmission gateway 100 transmits a data packet to the receiving device C12, and thereby reduction in the TCP window size under the circuit L12's transmission cost burdens has been prevented, a falloff in the system's throughput eliminated, and deterioration in the speed performance suppressed.
Moreover, when it receives a data packet from the transmission unit, the transmission gateway 100 prepares a temporary delivery acknowledgement and retains the data packet until a delivery acknowledgement (ACK) is received from the transmission unit, and only when three identical delivery acknowledgements (duplicate ACK) are received does the transmission gateway decide that the data packet transmission is a failure and proceed to retransmit the retained data packet.
Under the conventional data distribution management system, however, the existence of the data segments whose protocols are not influenced by transmission delays is not considered, nor is the existence of the data segments of which the protocols deteriorate in transmission efficiency once a temporary delivery acknowledgement is used. This plus the conventional practice of sending a temporary delivery acknowledgement to the transmission device C11 with respect to all data segments, has increased the processing load on both the transmission gateway 100 and the transmission device C11, and conversely, often deteriorates their speed performance to a problematic extent.
Furthermore, in conventional practices, temporary delivery acknowledgement is sent to the transmission device C11 with respect to all data segments, and therefore even when erroneous data segments are received from the transmission device C11 as are those data segments which are interpreted as data segments of other than BGP or windows type, a temporary delivery acknowledgement is invariably sent to the transmission device C11 to often result in contradictions arising in communication, in which case the processing load on the transmission gateway 100 and on the transmission device C11 increases so much so that the problem of deteriorated speed performance crops up.
Additionally, the delivery acknowledgements sent from the receiving device C12 are wholly abrogated at the transmission gateway 100 and are in no case transferred to the transmission device C11. Therefore, when data is transmitted in so-called piggyback fashion in which delivery acknowledgements transmitted from the receiving device C12 are included in the data segments transmitted from the receiving device C12 to the transmission device C11, there emerges a problem such that the data segments from the receiving device C12 to the transmission device C11 do not reach the transmission device C11.
Accordingly, it is an object of this invention to provide a data distribution management device and a data distribution management method capable of eliminating the contradictions involving communications between a transmission unit and a receiving unit, reducing the load involving the preparation and transmission of temporary delivery acknowledgement, and performing further high-speed and correct data distributions.